The subject matter disclosed herein relates to energy production and, in particular, to controlling energy production facilities in the presence of variable production capabilities.
The production of energy in the form of electricity may take many forms. At the center of nearly all power stations is a generator, a rotating machine that converts mechanical energy into electrical energy by creating relative motion between a magnetic field and a conductor. The energy source harnessed to turn the generator varies widely. One energy source is wind.
A wind farm is a group of wind turbines in the same location used for production of electric power. Individual turbines are interconnected with a medium voltage (usually 34.5 kV) power collection system and a communications network. At a substation, this medium-voltage electrical current is increased in voltage with a transformer for connection to the high voltage transmission system. The high voltage transmission system is often referred to as a “grid.”
A large wind farm may consist of a few dozen to about 100 individual wind turbines, and cover an extended area of hundreds of square miles (square kilometers). A wind farm may be located off-shore to take advantage of strong winds blowing over the surface of an ocean or lake.
As is well known, electricity generated from wind can be highly variable at several different timescales: from hour to hour, daily, and seasonally. Annual variation also exists, but is not as significant. Because instantaneous electrical generation and consumption must remain in balance to maintain grid stability, this variability can present substantial challenges to incorporating large amounts of wind power into a grid system. Intermittency and the non-dispatchable nature of wind energy production can raise costs for regulation, incremental operating reserve, and (at high penetration levels) could require an increase in the already existing energy demand management and load shedding. However these challenges are no different in principle to the substantial challenges imposed by other forms of generation such as nuclear or coal power, which can also show very large fluctuations during unplanned outages and have to be accommodated accordingly.
Currently, wind farms are operated based on the “ramp rates” of the particular wind turbines. The ramp rate for a particular turbine (or collection thereof) is expressed in kilowatts/second and represents the rate of change in power production that the wind turbine can provide at normal operating conditions. Each individual turbine may have a ramp up rate and a ramp down rate representing, respectively, the change band of upper and lower limits of the power production of the turbine. The wind farm as a whole may have a total output referred to herein as the farm ramp rate (RRfarm), which is the aggregate of all of the power change provided to the power collection system.
Utility companies in general, and those connected to a wind farm in particular, have the requirement to keep the power grid they create out of fluctuations caused by high produced power changes. That is, there may be spikes in RRfarm caused by increases in wind rate that need to be avoided.
In the even that wind speed increases, the additional power created may be shed so that the wind farm as a whole produces a constant output. The shedding may be accomplished by ramping the power output down from one level to another. That is, the conversion rate of one or more of the wind turbines is ramped down (based on a ramp down signal) from one level to a lower level to create a lower power output. This, however, leads to the loss of power that could otherwise have been created by the wind turbine if running at a higher conversion rate.
In the event that wind decreases, the efficiency is ramped up to meet the output demands (based on a ramp up signal). That is, the conversion rate of one or more of the wind turbines is ramped up from one level to a higher level to create a power output that meets the demand. However, in the event of a large decrease in wind, regardless of conversion efficiency, at present there may be no way to meet the power production demands. Thus, the utility must find other ways to provide the needed power. This may include, for example, including a diesel generator at the wind farm that is brought on-line when wind speed decreases in an attempt to keep RRfarm at or above the desired rate.